Only a few months after giving birth to her first child, Scarlett Johansson already looks in superhero shape. Just how did the "Avengers: Age of Ultron" star pull it off? 

"[Breastfeeding is] the best way to get back in shape," Johansson told Barbara Walters during a taping for her "10 Most Fascinating People of 2014" special. "[I do] the whole bit. I'm nursing and I love it."

Like any other first-time parent, the 30-year-old actress said that while becoming a mother has been "wonderful" and "very, very, magical," it's also been "exhausting." Nevertheless, the star told that her workout routine really hasn't changed much since the arrival of her daughter; it's just about finding time.

"I do the same fitness routine as my big muscle-man trainer," she said. "A lot of it is endurance, stability, and strength training. I like to work up a sweat. I've tried Pilates and yoga and all that, and I like to dabble in different things, but I always come back to a good old-fashioned athletic, full-body workout."

As for Johansson's endorsement for breastfeeding as a weight loss strategy, there is research to support it, but results vary depending on the woman's metabolism, pregnancy weight gain and post-pregnancy diet and exercise routine. 

"A lot of women say it helps with a lot of the weight up front, but the last 10 pounds, if you’re breast-feeding, are very hard to lose," Tanya Zuckerbrot, M.S., R.D. told Women's Health. "It’s understandable for women who only gain those 25 pounds to be back in their skinny jeans two months later because you can lose 10 pounds in two months, whether you’re breast-feeding or not."

Zuckerbrot recommends pregnant women keep their weight gain in check (25-30 pounds) and post-pregnancy embrace a diet high in fiber (fruits, vegetables and whole grains), protein and plenty of water.

Walters "10 Most Fascinating People of 2014" special airs this Sunday on ABC at 9:00 p.m.

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Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Scarlett Johansson credits breastfeeding for post-pregnancy weight loss
Actress describes motherhood as 'very, very magical,' but equally 'exhausting.'